Field of the Invention
The present invention relates to a surface treatment method and a coating method for a steel material, and to a method for producing a machine component.
Description of the Related Art
In recent years, the machine components used in hydraulic excavators and other such construction machinery have been subjected to various surface treatments as precoating preparation to improve the adhesion and corrosion resistance of the coating.
For example, there is a surface treatment method for a steel material that involves the use of a treatment liquid containing zinc phosphate and that comprises a degreasing step, a first water washing step, an acid washing step, a second water washing step, a neutralization step, a third water washing step, a surface adjustment step, a fourth water washing step, a chemical conversion coating step, a fifth water washing step, and a hot water washing step.
However, a problem is that the treatment liquid containing the zinc phosphate also contains a large amount of heavy metal ions, which are harmful to the environment. Also, because zinc phosphate itself is a deleterious substance, there is a problem of higher costs required by the need for special equipment to perform this treatment (see Japanese Laid-Open Patent Application 2010-106334 (laid open on May 13, 2010), for example).
Accordingly, treatment liquids whose main component is malic acid, orthophosphoric acid, or the like have been developed as treatment liquids that are more environmentally friendly and safer for workers to use, and these have been used in the surface treatment of some parts.